When constructing a building wall made from masonry blocks, masons normally erect guide blockwork at the corners of the wall. The guide blockwork at each corner is typically referred to as a lead corner. From these lead corners, a guide line is stretched to facilitate the laying and leveling of the remaining blocks.
One primitive method of trigging the guide line is to drive a nail or spike into the mortar between the blocks of opposite lead corners and then tightly stretch the guide line between the nails or spikes. If the guide line is stretched too tightly, the mortar can crack and cause the guide line to sag, thereby inhibiting the laying of a straight and level wall.
In an effort to improve upon the primitive trigging method described above, numerous more sophisticated techniques have been developed to trig the guide line. These prior techniques are not completely satisfactory because they utilize devices which require either (i) construction of lead corners or a substantial portion of a course (see, for instance, U.S. Pat. Nos. 402,360; 441,492; 614,577; 1,092,058; 2,685,741; 2,728,142; 2,761,214; 2,788,579; 2,833,043 and 3,397,458) or (ii) repositioning in order to lay multiple courses (see, for instance, U.S. Pat. Nos. 995,714; 2,659,973; 2,665,487 and 3,148,453). The construction of lead corners or a substantial portion of a course is time consuming and therefore undesirable. It is also time consuming and therefore undesirable to resposition the trigging devices after each course has been laid.